A case of Rhodococcus equi brain abscess

Current taxonomy of Rhodococcus species and their role in infections

Rhodococcus is a genus of obligate aerobic, Gram-positive, partially acid-fast, catalase-positive, non-motile, and none-endospore bacteria. The genus Rhodococcus was first introduced by Zopf. This bacterium can be isolated from various sources of the environment and can grow well in non-selective medium. A large number of phenotypic characterizations are used to compare different species of the genus Rhodococcus, and these tests are not suitable for accurate identification at the genus and species level. Among nucleic acid-based methods, the most powerful target gene for revealing reliable phylogenetic relationships is 16S ribosomal RNA gene (16S rRNA gene) sequence analysis, but this gene is unable to differentiation some of Rhodococcus species. To date, whole genome sequencing analysis has solved taxonomic complexities in this genus. Rhodococcus equi is the major cause of foal pneumonia, and its implication in human health is related to cases in immunocompromised patients. Macrolide family together with rifampicin is one of the most effective antibiotic agents for treatment rhodococcal infections.

Rhodococcus equi infection in HIV-infected individuals: case reports and review of the literature

Rhodococcus equi is a gram-positive, coryneform bacterium that causes zoonotic infection mainly in horses and foals. It sometimes affects humans presenting as cavitary pneumonia. Immunocompromised patients, including HIV-infected patients, are more susceptible to R. equi infection. We present 10 cases of R. equi infection in HIV-positive patients admitted to our institute from 1991 to June 2008. Moreover, we have reviewed 272 cases of R. equi infection in HIV-infected persons, published from 1986 through 2008. With respect to the literature data, the R. equi strains isolated in our case series showed lower sensitivity to ceftriaxone, amoxicillin/clavulanic acid, and cotrimoxazole. Prompt diagnosis, early initiation of antiretroviral treatment and combined antimicrobial treatment seem to be effective to eradicate the infection and to improve the outcome.

Molecular and infection biology of the horse pathogen Rhodococcus equi

The soil actinomycete Rhodococcus equi is a pulmonary pathogen of young horses and AIDS patients. As a facultative intracellular bacterium, R. equi survives and multiplies in macrophages and establishes its specific niche inside the host cell. Recent research into chromosomal virulence factors and into the role of virulence plasmids in infection and host tropism has presented novel aspects of R. equi infection biology and pathogenicity. This review will focus on new findings in R. equi biology, the trafficking of R. equi-containing vacuoles inside host cells, factors involved in virulence and host resistance and on host-pathogen interaction on organismal and cellular levels.

Rhodococcus equi brain abscess in a patient without HIV

Rhodococcus equi, a Gram positive organism, is a cause of infections in immunocompromised individuals. In humans, it mainly causes disease in those infected with human immunodeficiency virus (HIV), and generally presents as chronic pulmonary infection. It may also cause intracranial infections, which manifest as brain abscesses. This report describes a case of rhodococcus brain and pulmonary infection in a patient who did not have HIV or another disorder of cell mediated immunity. He was treated with intravenous imipenem, vancomycin, and rifampin for eight weeks and recovered from the infection.

Gordona terrae central nervous system infection in an immunocompetent patient

The bacterial genus Gordona includes seven species of mycolic acid-containing actinomycetes which are cultured from environmental sources and rarely from clinical samples. They have been implicated in primary pulmonary diseases, nosocomial wound infections, and central nervous system infections in two immunocompromised patients. We isolated Gordona terrae from the cerebrospinal fluid sample of an immunocompetent patient with meningitis and multiple brain abscesses and detected Gordona terrae DNA in the abscesses. The outcome was good at the 4-year follow-up, after prolonged treatment with trimethoprim-sulfamethoxazole. Phenotypic identification of this isolate was confirmed by analysis of the 16S rRNA gene sequence, which shared 100% homology with that of G. terrae reference strains. Physicians and clinical microbiologists must be aware of the occurrence of Gordona species infection not only among immunocompromised patients but among all patients. Accurate identification of Gordona species may be accomplished by molecular techniques.

Rhodococcus equi infection in HIV-positive subjects: a retrospective analysis of 24 cases

Rhodococcus equi causes a rare infection in immunocompromised hosts. We describe 24 cases of infection in patients with AIDS-related complex (ARC)/acquired immunodeficiency syndrome (AIDS). Pneumonia was always the first manifestation of R. equi infection, but extrapulmonary involvement was also observed. The main sources of bacteria were sputum, bronchial washings and blood. The strains isolated were mainly susceptible to erythromycin, vancomycin, teicoplanin, rifampicin, imipenem and aminoglycosides. Initial treatment should involve an intravenously administered antibiotic combination therapy including imipenem or vancomycin or teicoplanin, followed by orally administered maintenance combination therapy. Drug combinations should be investigated for serum bactericidal activity in vitro. Surgery does not increase survival time and should only be performed in cases that do not respond to antibiotic treatment. Presumptive risks of infection (contact with horses or farm dust, or cohabiting with people affected by R. equi infection) were present in more than 50% of patients. This finding, and the frequency of bacteria in the sputum, are not sufficient proof of transmission between humans, but do suggest the need for respiratory isolation of patients affected by R. equi pneumonia.

Tamponade due to Rhodococcus equi in acquired immunodeficiency syndrome

Infection with Rhodococcus equi has been described as a cause of cavitary pneumonia in AIDS patients. We report such a case, complicated by bacteremia, tamponade, and possible brain and liver abscesses. Medical treatment was successful with pericardiocentesis and antibiotherapy with teicoplanin, gentamicin, clarithromycin, rifampicin, supplemented by empirical treatment of cerebral toxoplasmosis. Antibiotherapy was terminated after 6 months, without relapse 2 months later.

Successful medical therapy of Rhodococcus equi pneumonia in a patient with HIV infection

A 34-year-old HIV-infected man was successfully treated with antimicrobial therapy alone for Rhodococcus equi pneumonia and has survived longer than six months. In the current literature, only two of seven HIV-infected patients so treated have survived as long as six months. Based on our experience and the available literature, it seems reasonable to treat HIV-infected patients with R equi pneumonia who do not require surgical intervention with prolonged intravenous therapy followed by long-term oral therapy with at least two effective antibiotics. The optimal choice and duration of antibiotic therapy need to be determined.